Perturbative treatment of local correlations in Cu-0 planes for high temperature superconductors

Useful information about the high temperature superconductors might be obtained by studying the low-dimensional models in which the interplay between the short-range correlations and the geometry of the electron motion is taken into account. Here the short-range correlations are treated as a perturbation to 2-dimensional Cu-0 electrons. After defining the model Hamiltonian, the properties of the unperturbed part are briefly discussed and the perturbation expansions for various physical quantities are formulated. The low-order expressions for the self-energy, the magnetic susceptibility and the pair correlation function are presented which should, in principle, allow a systematic study of the effects of the Coulomb interactions on the properties of the model.